PRIME Minister Boris Johnson was ill-advised to prorogue Parliament, but it could be problematic for the Supreme Court to exercise a judgment on whether or not the act was lawful, a legal expert has said.

Speaking to BBC Radio 4's Today Programme, Stephen Tierney, Professor of Constitutional Theory at Edinburgh Law School, said: "Papers submitted suggest the request made by the Privy Council that the Queen prorogue Parliament was clumsy and inappropriate."

Tierney spoke out as the Supreme Court case on the prorogation resumed in London with QC Sir James Eadie outlining the Prime Minister's case. 

Judges are ruling on two appeals, one by campaigner Gina Miller's team and one by the government contesting last week's Court of Session ruling that Johnson's actions were unlawful. 

Tierney said: "It is a mistake to think that the crown, in this case represented by the Prime Minister, and Parliament are separate. We must understand that these two institutions work together.

"The Prime Minister can only make laws with the consent of Parliament. The executive sits in Parliament and is controlled by Parliament, and that is how the Crown has been constrained for 300 years.

"Our constitution prescribes appropriate jurisdictional limits ... If the court feels it can review prorogation, why would it not review legal statutes as well?"

On whether the Supreme Court should make a judgment on the prorogation of Parliament, Tierney added: "The court should not take this road. It is for Parliament alone to demarcate its sovereign relationship with the crown."

At least 40 people were already queuing to watch the second day's proceedings at the Supreme Court at around 8am. Two men at the front of the queue said they had been waiting since 6.30am.

Lord Wilson asked Eadie why no statement had been provided to explain why the prorogation decision was taken.

He adked: "Isn't it odd that nobody has signed a witness statement to say 'this is true, these are the true reasons for what was done'?"

Eadie replied: "My lord, we have the witness statements we have. My submission is that, in light of the case law only, it remains open to the court to make judgments on the facts on the basis of the underlying documents that have been produced."

Eadie said the documents provided to the court were from the "top level" of Government and included a note of cabinet discussions on prorogation.